Christy Walton

Net worth: $28.2 billion

Country: U.S. Source of wealth: Wal-Mart

Christy Walton's net worth reached new highs as Wal-Mart stock jumped in 2012. She remains the richest woman in the United States. Christy inherited her wealth when husband John Walton, a former Green Beret and Vietnam war medic, died in an airplane crash in 2005.